Luminescent apparatus and method of developing luminescence



2, 1946. H. w. LEVERENZ 2,403,227,

LUMINESCENT APPARATUS AND METHOD OF DEVELOPING LUMINESCENCE Filed Aug. 16, 1941 {k I I l l A ill??? vvvi iis a Patented July 2, 1946 LUMINESCENT APPARATUS METHOD OF DEVELOPING LUMINESCENCE Humboldt W. Leverenz, South Orange, N. J.,'assignor. to Radio Corporation of America, a corporation of Delaware Application August 16, 1941, Serial No 407,139

My invention relates to luminescent apparatus and particularly to tubes and systems wherein a luminescent phosphor screen is scanned by beams of radiant energy, such as cathode ray beams. Luminescent tubes are known wherein a 5 method of developing luminescent light having luminescent phosphor Screen is provided for defluorescent and phosphorescent components over veloping light under scansion with an electron n extended area in a predetermined scanning beam other beam of radiant energy. Such as sequence including a step of extinguishing the ultra-violet light beam. Such phosphor screens phosphorescent component of the luminescent are characterized in that, when excited by the light during a predetermined time following the radiant energy, light is liberated in response excitation of the fluorescent light. Further in thereto which is useful in portraying the path accordance with my invention I provide suitable of the beam or occurrences during its traversal apparatus for performing my method incorporatof the screen in which case the beam of radiant ing a composite luminescent screen scanned on energy may be modulated in accordance with an opposite sides by beams of radiant energy sepunknown phenomena. Such tubes are in extenarated'in-tim'e sequence, one component of the sive use for the recreation of television picture phosphor screen scanned by one beam having a replicas. Hereafter I will use the term luminesdefinite spectral emission with respect to. that cence to refer to the light and the property of ofthe phosphor component scanned by the second a phosphor developing light in response to inbeam. cident energy excitation, and I will use the term These andother objects, featuresand advanfluorescence to refer to the light developed durtag esofmy invention will become apparent when ing excitation, and the term phosphorescence considered in view of the following description to refer to the light liberated by a phosphor subof my apparatus'and method of operation when sequent to or following the cessation of excitag5 taken in connection with the accompanying tion. The term luminescence will therefore be drawingwherein: used to include both fluorescence and phos- Figure I shows a type of; tube andapparatus phorescence. made and operated in accordance with myin- The majority of luminescent screens are charvention and partic Suited to y method of acterized in the fact that they exhibit both fiuodeve op rescent and phosphorescent properties, the lib- Figure 2 is an enlarged View of p s te erated light intensity after cessation of excitation phosphor screen. suitable for use in the tube of often being a considerable percentage of the fluoi l; n rescent light intensity liberated during excita- Figure 3 shows the enclosed outline of a target tion. This fact as well as the fact that the fluoarea scanned by an electron beam together with rescent and phosphorescent light may be of diftwo phosphorescent decay curves expl ning my ferent colors is well known. For many applicainvention. tions of such tubes this inherent property of a WhileIwill describe one particular embodiment phosphor to exhibit both fluorescence and phos- .of an apparatus suitable for performing my methphorescence is a definite disadvantage in that the 40 0d of deve opin luminescent l ght, it will be phosphorescence may mask the phenomena which appreciated that my method of operation is not it is desired to portray by means of the fluorescent limited to the particular embodiment set forth characteristics of the phosphor. hereinafter, but that the method may be per- It is, therefore, an object of my invention to fo ed w other yp of pp s nd in a provide luminescent apparatus wherein the efmay be performed entirely by hand. Such an fects of fluorescence and phosphorescence may embodiment of y method l bodosoribod be differentiated. It is another object to 'prolowing the particular references .to the apparavide a tube and method of operation wherein the tus shown in "Figure 1 wherein the tube I comphosphorescence of the material may be conprises: an evacuated envelope having two neck trolled or minimized in a definite time sequence portions 2 and 2" and an intermediate cylindrical with respect to the excitation of the phosphor portion 3 enclosing a composite phosphor screen to fluorescence. It is a still further object to which ;will be described'hereinafter in considerprovide a tube wherein masking of the fluorescent able detail as, to its preferred components, and light by the phosphorescent light is avoided withmethod of construction. 'Th composite phosout diminution of the fluorescent light, and it is 13 Claims. (01. 250-) a'still 'iurther object to provide a tube wherein the effective period of phosphorescence may be limited to a predetermined length of time.

In'accordance with my invention I provide a phor screen! is so ;pos itioned. that lt' may be scanned by an electron beam on each side thereof, such as developed by electrode structures located within the neck portions 2 and 2. The electron beam developing means positioned in each of the neck portions 2 and 2' may be substantially identica1 and include cathodes -55' preferablyof the type which may be indirectly heated by a filamentary heater. The cathodes 5-5' may each be surrounded by a control grid or intensity modulating electrode 6--6f connected.

to the usual biasing battery, such asthrougna potentiometer as shown, and to the negative terminal of the potential source 1. Itwill'be. appreciated that the control e1ectrode-leads -may be provided in series with a source of modulating potential 8-8 although for certain applications to which my method and system is particularly adapted it is necessary to apply modulating :potentials to only one of the grid electrodes, such as the grid electrode 6. However, for other applications the modulating sources may be entirely eliminated. The electrons liberated by the oathodes 55 and controlled by the electrodes 6--6 are accelerated and directed toward opposite sides of the phosphor screen 4 by first anodes 99 connected to an intermediate point on the potential source 1 for purposes of beam focusing and by second anodes 10-40 connected to the positive terminal of the potential source I so that the beam comprisingthe electrons is focused on the luminescent phosphor screen 4. Intermediate the anodes 9--9' and the screen 4 an preferably surrounding the respective neck portions 2-4, I provide mutually perpendicular deflection means, such as the vertical deflection coils I ll l and horizontal deflectioncoils l-2l2', to deflect each of the beams over .the extended area of the screen 4 in sucha manner that. the areas scanned ing different spectral emission characteristics.

The layer I5 maybe of any suitable material havingpeaked .spectral emission characteristics in the visible or ultraviolet portions of the spectrum "and. may be those materials having relatively great a phosphorescence Various inorganic'phosphors, such as manganesefollowing excitation.

activated zinc silicate, zinc beryllium or zirconium by one beam on one side of the screen are directly opposite the areas scanned by the other beam but at a somewhat .later predetermined time. The deflection coils II. and I2. are. connectedto a conventional deflection supply. circuitshown at l3. This deflection supplyrcircuitmay comprise conventional sawtooth generatingxcircuits .or may comprise a time axissupply connected to. one set of coils with an unknown waveform applied to the other set of coils. Similarly the deflecting coils ll-l2' may be connected toagseparate conventional source of deflection supply ascircuit shownat l3 which may likewise develop sawtooth current forms under control of the deflection supply 13 in such a manner that the electron beam from the cathode 5' scans over the same areas on the right side of the screen 4 as the areas scanned on the left side but at a predetermined time following the scanning on the left side. Obviously electrostatic means may be substituted in whole or in part for the magnetic means for beam deflection and means may be provided for keystone correction, which is desirable when the electron beam scans an inclined target.

In accordance with my invention I provide a luminescent phosphor screen 4 either as shown in Figure 1 or Figure 2 comprising a compositephosphor or phosphor coated member. In 1 either event the screen 4 is so positioned that it may be viewed by an observer at I4, although where both electron guns are angularly displaced the screen may be viewed such as by an observer at H, as referred to more particularly below. More particularly the structure sh0Wnin*Figure 2 may comprise a luminescent phosphor screen having two layer components, such as the phosphor layer silicate, copper or silver activated zinc or cadmium sulphides or various other materials having a visible spectral emission under excitation may be used for the layer [5. I provide the layer l5, however, ofa material having relatively rapid phosphorescent decay characteristics with high luminescence, such asin the red or infrared portions of the spectrum, capable of ,accelerating or extinguishing the phosphorescence of the material comprising layer 5. The material comprising the layer I5 is preferably chosen to have the same or somewhat shorter phosphorescence than the layer l51and may to, advantage comprise chromium activated aluminum oxide, chromium activated. aluminum berylliate, ,chromium activated, Zinc-beryllium ,alum-inate and manganese activated magnesium silicate. All of these materials, have ,an excitation band in the red or infra-redportions of, the spectrum so that the lightliberatedby the elemental scanned areas of the layer vI5'gbecomes incidentuponopposite areas of the layer 15. *,Such oppos'iteareas-having been. previously scanned by-the beam ,1 fiqmay still be liberating phosphorescent light, andthe luminescence ,fromthe;lay er -I 5", rapidly, acceleratesthis liberation of ,light thereby rapidly ex- .tinguishing. the phosphorescence-from thevlayer accurately these factorsgarevchosen so, that. .the

electron beam, does; not penetrate to,,any.:;large extent into and excite the-layer ,underlyingvthe layer scanned by the-particuIarIy,electronbeam.

layer to anotherxwhich might excitethe other layer, the phosphor layers 15 and I 5'. maybe sep- ..arated byv a small but finite distance on opposite 1 sides of an electron barrier 11. Thus; as shown in'Eigure 1 the layers I5 and I5'-- may beon-opposite sides of a thin lass or otherinf-ra-red transparent electron barrier I 1 serving as a foundation for the two layers. The separation between'the the electron beam diameter to prevent loss of resolution. Otherwise spreading of the luminescence from the layer l5 tends to accelerate the value-at the polntG'. The electron beam l6,

extinction of phosphorescence before such action is desired.

I have referred above to the use of cascade phosphor layers, the principal mode of operation of which is fully'described in my copending application, Serial No. 383,893, filed March 18, 1941. Such screens in principle comprise a series of layers of different phosphor materials having different spectral emission characteristics-and related spectral absorption characteristics whereby, following excitation of one layer, the'second layer is excited at a lower frequency by the lu-- minescent light of the preceding layer. Such a multiple cascade phosphor system may be substituted for the layer l5, with the layer of the cascade having the highest frequency or shortest wavelength spectral response facing the electron beam 16 and the layer having the lowest frequency spectral response facing the layer l5. In

such a combination the layer l 5' is of a phosphor having a lower frequency or longer wavelength spectral response than the nearest adjacent-layer of the cascade screen.

The various chromium and manganese'activated materials referred to above are suitable for use with phosphor layers of either the single or cascade type having a useful emission spectra over a wide range of frequencies and I have chosen these phosphor materials because their spectral absorption band lies outside of the visible spectrum so that the composite screen may be viewed from the scanned side of the layer I5 such as by an observer at I4. If, however, the layer I5 is to be observed directly such as by an observer at I4, the layer l5 may comprise phosphors having absorption spectra overlapping the emission spectra of the layer or layers I5; Such phosphors include silver or copper activated zinc-cadmium sulphide of relatively high cadmium content and silver or copper activated zinc sulpho-selenide.

In operation of my method and system elemental areas of the layer, or series of layers represented by the layer l5, are scanned in a predetermined sequence, such as by the electron beam I6, elemental areas of the layer l5 opposite u said elemental areas of the layer l5 being scanned at a predetermined time later for the purpose of extinguishing the phosphorescent light developed by the layer l5. This scanning sequence and the resultant action will be fully appreciated by reference to Figure 3 wherein the lines AB,' CD and EF represent three elemental lines scanned on opposite sides of the phosphor screen 4 by the two electron beams. It will be assumed that electrons are simultaneously scanning widely separated areas at any instant of time for which the instantaneous position of the beam I6 is shown at point G and the instantaneous position of the electron beam I6 is shown at G. The

dashed-line curve originating at the point G representative of the phosphorescence developed howeven'from the cathode 5' has reachedthe point G along the scanning line AB at the time theelectron beam l6 has reached the point. G. The electron beam l6 produces luminescence of which the phosphorescent component is shown by the dash-dot line of Figure 3. This phosphorescent component is light of low frequency, preferably being in the red or infra-red portion of the spectrum and is usually of lower frequency than'the phosphorescent light from the layer l5. Consequently the light from the layer, I5 is incident upon the layer I5 at the point G and since the phosphorescence of the layer IE3 at the point G is "still of finite value, the energy developing the phosphorescence in the layer 15 at thepoint G is rapidly dissipating as shown by the hump ln'the curve following the point G. The phosphorescence of the layer 15 following the point G' is, therefore, rapidly accelerated andextinguished and becomes practically zero at the point I-I so that from H to A of the scanning line AB and from F-to G of the scanning line :EF the screen l5.is developing no useful light. 'Obviously this arrangement allows the positive extinction of the phosphorescent light' developed by the layer l5 prior to the redevelopment of luminescen'ce by the scanning beam l6. Consequently the period of phosphorescence of the line l5'may be controlled over a wide time range, limited only by the maximum time period between sequential scanning of the same area andaminimum time period necessary for the extinction of the phosphorescence by the beam [6 represented by the scanning time between points G and H.

As shown by Figure 3 the phosphorescent de- From the above it will be evident that I have provided a system and method whereby the period of phosphorescence of a luminescent screen may be controlled within definite time limits and .that the extinction of the phosphorescence may be limited to confined areas. Previous arrangements for the extinction of phosphorescence have limited the useful light output of the device. Thus, it has been proposed to utilize a filter transparent to fluorescence but opaque to phosphorescence or to-use a flood of infra-red light over the entire phosphor screen area to extinguish the phosphorescence. Obviously such arrangements are definitely disadvantageous in that they are continuously effective and considerably decrease the light output which may be utilized to advantage.

While I have described my system and method with particular reference to phosphor excitation by'cathode ray beam means and with particular reference to a preferred structure utilizing electron beam generating means it will be appre- I ciated that my method and apparatus is notllimphosphor screen wherein the ultra-violet light is I scanned by the use of mirrors or by a scanning spot from a cathode ray tube having an ultraviolet emitting phosphor screen. Furthermore, my method may be performed efliciently by manually moving; alight" beam' from, flashlights held in the hand by each of two persons on opposite sides of a composite phosphor screen in such a manner that the light beam developing the longest wavelength light on the phosphor'screen fol lows the other light beam. Therefore, inview of these many modifications in apparatus and the fact that various expedient-s may be utilized in following'my method, my invention should not be limited to the particular apparatus or to the sequence of steps described except as set. forth in the appended claims.

Iclaim:

1. Apparatus for developing luminescent light comprising a luminescent target having phosphor material exposed on opposite sides thereof, means facing each side of said target to subject each of said sides to a beam of luminescence exciting energy, the said phosphor material on one side of said target having a spectral emission, when excited, of higher frequency than the said phosphor material on the other side of said target and means to scan said beams of exciting energy over similar paths on opposite sides of said target and at non-opposite points at any instant of time along said paths.

2. Apparatus for developing luminescent light and extinguishing phosphorescent light comprising a composite phosphor screen of extended area, said screen including oppositely disposed phosphor materials excitable to luminescence under incident excitation at different wavelengths, means to scan elemental areas of the extended area of the phosphor material excitable at the shorter'wavelength with a beam of radiant energy to develop luminescence including a phosphorescent component, and means to scan elemental areas of the other phosphor material" opposite said first-mentioned elemental areas at a time within the phosphorescent decay period following scanning of said first scanned material.

3. Apparatus for developing luminescence and suppressing phosphorescence comprising a luminescent screen having oppositely disposed layers of phosphors, one of said phosphors having a luminescent excitation band of relatively high frequency, the other phosphor having a band extending into the infra-red portion of the spectrum, and means to scan opposite elemental areas of said phosphors during sequential periods of time wtih luminescence exciting energy whereby the phosphorescence of the high frequency emitting phosphor is accelerated.

4. Apparatus for developing luminescence and suppressing phosphorescence comprising, a luminescent screen having oppositely disposed-layers of phosphors, one of said phosphors having a luminescent and phosphorescent,excitation band of relatively high frequency, the other phosphor having an excitation band extending 'into the infra-red portion of the spectrum, and means to scan opposite elemental areas of said hosphors with luminescence exciting energy during sequential periods of time, the scanning of the high frequency phosphor preceding the scanning of the said other phosphor whereby the phosphorescence of the high frequency emitting phosphor is accelerated.

5. Apparatus as claimed in claim 4 wherein the phosphor having a relatively high frequency excitation band is of a material having a longer phosphorescent decay time than that of the phosphor having a band extending into the infra-red portion of the spectrum.

;6.=1; Apparatus for developing luminescent light.

-.8 "comprising an evacuated .envelope, .a pair of opm positely ,disposed; electron sources in jsaid envelope a :composite luminescent phosphor screen having a phosphorescent material excitable under incident electrons in the visible portion of the spectrum facing .one .of. said electronsources .anda material xcitable in the infra-red-portion of the spectrumfacing theother of. said-sources, means-to scan electrons over elemental, areas of said first-mentioned material to excite visible luminescence including a phosphorescent light component andmeans.toscanelectrons from said secondsource over- ..elementalareas. of said second-mentioned material opposite. said first-rmentioned areas within a, time, following .said i firstmentioned scanning less than the-phosphorescent decay period of said-.firstementioned material.

LApparatus for developing luminescent..light and suppressing phosphorescent light comprising anevacuated enve1ope, .a,..pair of oppositel ,disposed electron sources .insaid-envelope, a.c0mposite luminescent ,phosphor screen having a layer of phosphorescentmaterial excitable under incident electrons inthevisibleportion ofthe spectrum facing-one of saidelectronsources and a layer of material excitable .inthe. infra-red portion of the spectrum facing the other of said sources, means to scan electrons over elemental areas of said first-mentioned material layer to excite visible luminescence including a phosphorescent light component, means to scan electrons from said second source over elemental areas of said second-mentioned material layer opposite said first-mentioned areas within a time. following said first-mentioned scanning less than the phosphorescent decay period of said first-mentioned material and means between said material layers to prevent excitation of one material. layer by electrons incident upon the other material layer.

8. Apparatus for developing luminescent light comprising a luminescent phosphor layer of material excitable under incident energy in the visible portion of the spectrum, asecond layer contiguous with said first layer excitable and emitting energy in the infra-red portion of the spectrum, dual means tosequentially subject directly opposite elemental areas of said layers to incident luminescence exciting energy the time period between excitation of opposite areas being within the phosphorescent decay time of said first-mentioned layer, and means to prevent undesirable excitation of both of said layers by one of said dual means.

9. Apparatus for developing luminescent light comprising a luminescent phosphor layer of material excitable under incident energy in the visible portion of the spectrum, a second layer contiguous with said first layer. excitable and emitting energy in the infra-red portion of the spectrum, dual means to sequentially subject directly opposite elemental areas of said layers to incident luminescence exciting energy the time period between excitation of opposite areas being within the phosphorescent decay time of said first-mentioned layer, each of said layers being of sufiicient thickness to absorb substantially all of the energy incident on the respective layers whereby undesirable excitation of both of said layers by each of said dual means is prevented.

10. The method of developing and controlling luminescent light comprising the steps of, developing luminescent and phosphorescent light'over displaced elemental areas, in space ingpredetermined sequence and developing: luminescence of longer wavelength than said developed light over elemental areas adjacent with said first-mentioned areas at a finite time following the first development of luminescence.

11. The method of developing and controlling the intensity of light comprising the steps of developing light having a fluorescent and a phosphorescent component over displaced elemental areas in space in predetermined sequence and developing luminescence of longer wavelength than the phosphorescent component of said developed light over elemental areas contiguous with said first-mentioned areas at a finite time following the first development of the fluorescent light component.

12. The method of developing light of predetermined phosphorescent decay period including the steps of developing phosphorescence over elemental areas displaced one from the other in coplanar relation, and developing light of longer 10 wavelength than said phosphorescence over elemental areas in coplanar relation and adjacent said first-mentioned areas during the unobjectionable decay period of said phosphorescence and at a finite time following the initial development of phosphorescence. I

13. The method of developingdight' of predetermined phosphorescent decay period including the steps of simultaneously developing fluorescence and phosphorescence over elemental areas displaced one from the other in coplanar relation, and subsequently developing fluorescence and phosphorescence of longer wavelength than the first developed phosphorescence over elemental areas adjacent said first mentioned areas during the decay period of said first developed phosphorescent light and at a finite time following the development of said first mentioned fluorescence.

HUMBOLDT W. LEVERENZ. 

